Wheel loader

ABSTRACT

A wheel loader includes a vehicle body having wheels a work implement including an arm, a bucket, and an arm cylinder and a bucket cylinder that drive the arm and the bucket, respectively, and a work implement control device that directs an operation of the work implement. The work implement control device includes an arm control lever disposed on the right of a driver&#39;s seat, the arm control lever controlling operations of the arm, and two kickdown switches disposed at an upper surface and a left side surface, respectively, of a grip of the arm control lever. Operability can thereby be improved even further.

TECHNICAL FIELD

The present invention relates to a wheel loader that scoops up and movesexcavated material.

BACKGROUND ART

Work implements of wheel loaders generally include an arm cylinder thatelevates an arm and a bucket cylinder that dumps or crowds a bucket. Aknown wheel loader includes, as control mechanisms for directingoperations of the arm cylinder and the bucket cylinder, two controllevers for operating the arm and the bucket, respectively. The twocontrol levers may, for example, be disposed on the right-hand side inthe cabin (hereinafter referred to as an “arm control lever” and a“bucket control lever”) (see, for example, patent document 1).

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1-   WO Publication No. 2010/147232

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

A typical sequence of wheel loader operations is as follows.Specifically, the wheel loader: (A) moves to a location near a mound ofsoil or other material to be excavated (hereinafter referred to as the“mound” as appropriate); (B) causes an open mouth of a bucket to faceforward and the bucket to penetrate into the mound with an arm lowered;(C) further advances with the bucket penetrating in the mound and, whileraising the arm, crowds the bucket to thereby scoop up the material tobe excavated with the bucket; and (D) with the material loaded in placein the bucket, reverses to be away from the mound, moves to apredetermined location, and dumps the material. Among the sequence ofthese operations, while emphasis is placed on fuel economy in theoperations of (A) and (D) in which no large running driving force(traction force) is required for thrusting the material, the operationsof (B) and (C) require a large running driving force for scooping up thematerial at appropriate timing.

Patent document 1 discloses a wheel loader arrangement that includes akickdown switch for quickly effecting a downshift and a mode changeoverswitch for temporarily canceling a restriction on the engine maximumspeed and thereby increasing the maximum running driving force (changingthe running mode), the kickdown switch being disposed at an upperportion of an arm control lever and the mode changeover switch beingdisposed at an upper portion of a bucket control lever, respectively.This arrangement enables a required large running driving force to beobtained by operating the kickdown switch to shift down to a lower shiftspeed when the operation is changed from (A) to (B), and an even largerrunning driving force to be produced by operating the mode changeoverswitch as appropriate according to the situation upon the operation of(C).

In a wheel loader of this type having two control levers for operatingthe work implement, one for the arm and the other for the bucket, thearm control lever needs to be operated for the operation of (B) and thebucket control lever needs to be mainly operated for the operation of(C).

The control operation to be performed during the operation of (B) isadjusting posture of the bucket and downshifting. These controloperations are to be performed preliminary to the excavating, requiringno delicate adjustments as the work progresses. The control operationscan be performed fairly easily with the operator resting his or her handonly lightly on the arm control lever. How the arm control lever isgripped varies depending on each individual operator. One may firmlygrip the arm control lever or rest his or her hand lightly thereon, orgrip the arm control lever from above or from a side.

The control operation to be performed during the operation of (C) is tocrowd the bucket and, in parallel therewith, advance the wheel loader,while raising the arm. In addition, in the operation of (C), the greaterthe maximum running driving force is not necessarily the better. Forexample, a large running driving force may be required for penetratingthe bucket into the material to be excavated; meanwhile, if the wheelloader is made to run with an excessively large running driving forcewhen running load of the excavated material is heavy, the wheels mayslip to gouge the road surface, affecting subsequent work. During theoperation of (C), while the bucket is crowded as the arm is raised, themaximum running driving force needs to be increased as necessary and, atthe same time, the foregoing situation is properly avoided.

As compared with the operation of (B), the operation of (C) requires amore delicate and concentrated control operation. Thus, more operatorstend to grip firmly to operate the bucket control lever.

The present invention has been made in view of the foregoing situationand in consideration of the present situation of control operationsperformed by an operator from a viewpoint of user friendliness and it isan object of the present invention to provide a wheel loader that canimprove control operability.

Means for Solving the Problem

(1) To achieve the foregoing object, an aspect of the present inventionprovides a wheel loader comprising: a vehicle body having a wheel; awork implement disposed at a front portion of the vehicle body; and awork implement control device for directing an operation of the workimplement, the work implement control device comprising: a control leverdisposed on a side of a driver's seat, the control lever being used fordirecting an operation of the work implement; and two switches disposedat an upper surface and a side surface of a grip of the control lever,the side surface of the grip being on a side adjacent to the driver'sseat, the two switches being used for performing operations associatedwith a traction force.

(2) In the arrangement of (1) above, preferably, the work implementincludes an arm, a bucket, and an arm cylinder and a bucket cylinder fordriving the arm and the bucket, respectively, and the work implementcontrol device includes: an arm control lever serving as the controllever, the arm control lever for directing an operation of the armcylinder; a bucket control lever in juxtaposition to the arm controllever on a side adjacent to the driver's seat, the bucket control leverfor directing an operation of the bucket cylinder; two kickdown switchesthat are the two switches disposed at the upper surface and the sidesurface of the grip of the arm control lever, the side surface of thegrip being on the side adjacent to the driver's seat, the two kickdownswitches for forcibly effecting a downshift of a shift speed position;and a mode changeover switch disposed at a side surface of a grip of thebucket control lever, the side surface of the grip being on a sideadjacent to the driver's seat, the mode changeover switch being used forchanging over a plurality of running modes having different enginemaximum speed upper limit values from each other.

(3) In the arrangement of (2) above, preferably, the mode changeoverswitch is disposed at an upper surface of the grip of the bucket controllever, in place of, or in addition to, the side surface of the grip ofthe bucket control lever adjacent to the driver's seat.

(4) In the arrangement of (2) or (3) above, preferably, the modechangeover switch is a pushbutton for individually directing achangeover of a plurality of running modes having different enginemaximum speed upper limit values from each other.

(5) In the arrangement of any of (2) to (4) above, preferably, the wheelloader further comprises display means for displaying a running modeselected with the mode changeover switch.

(6) In the arrangement of any of (2) to (5) above, preferably, the wheelloader further comprises a detent mechanism for maintaining posture ofthe arm control lever at a position at which an arm raising operation isdirected.

Effects of the Invention

The present invention can achieve even better operability by flexiblydisposing the kickdown switch and the mode changeover switch accordingto different modes of operation of the operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view showing a wheel loader according to anembodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a drivesystem disposed in the wheel loader according to the embodiment of thepresent invention.

FIG. 3 is a running performance diagram (torque diagram) showing arelation between an engine speed and torque when an accelerator pedal isfully depressed in the wheel loader according to the embodiment of thepresent invention.

FIG. 4 is a graph showing a relation between a vehicle speed and arunning driving force at each of different shift speeds in the wheelloader according to the embodiment of the present invention.

FIG. 5 is a plan view showing a configuration of a cabin in the wheelloader according to the embodiment of the present invention.

FIG. 6 is a schematic view showing a main switch for changing a runningmode in the wheel loader according to the embodiment of the presentinvention.

FIG. 7 is a schematic rear elevational view showing an appearance ofwork implement control devices in the wheel loader according to theembodiment of the present invention.

FIG. 8 is a schematic view showing how material to be excavated, such assand and gravel, is scooped up during loading of the material onto, forexample, a dump truck using the wheel loader according to the embodimentof the present invention.

MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below withreference to the accompanying drawings.

FIG. 1 is a side elevational view showing a wheel loader according to anembodiment of the present invention.

A wheel loader 100 shown in FIG. 1 includes a vehicle body 110 and awork implement 120 mounted at a front portion of the vehicle body 101.

The vehicle body 110 includes a front vehicle body 111 and a rearvehicle body 112. The front vehicle body 111 and the rear vehicle body112 include a front wheel (tire) 113 and a rear wheel (tire) 114,respectively. The front vehicle body 111 and the rear vehicle body 112are mutually bendably connected to each other via a center pin 115extending in a vertical direction. The front vehicle body 111 and therear vehicle body 112 are connected to a steering cylinder, not shown.With a telescopic drive of the steering cylinder, the front vehicle body111 bends to the right or left relative to the rear vehicle body 112. Acabin 116 is mounted at a front portion on the rear vehicle body 112 andan engine compartment 117 is mounted at a rear portion on the rearvehicle body 112. The engine compartment 117 houses therein, forexample, an engine 131 as a prime mover to be described later, ahydraulic pump 134 driven by the engine 131, and a control valve 135that controls a direction and a flow rate of hydraulic fluid deliveredfrom the hydraulic pump 134.

The work implement 120 includes an arm 121 and a bucket 122. The workimplement 120 further includes an arm cylinder 123 and a bucket cylinder124 for driving the arm 121 and the bucket 122, respectively. With atelescopic drive of the arm cylinder 123, the arm 121 is rotatedvertically (elevating). With a telescopic drive of the bucket cylinder124, the bucket 122 is rotated vertically (dumping or crowding).

FIG. 2 is a block diagram showing a schematic configuration of a drivesystem of the wheel loader 100.

As shown in FIG. 2, the drive system 130 of the wheel loader 100includes the engine 131, a torque converter 132, a transmission 133, thehydraulic pump 134, the control valve 135, a controller 136, an enginecontrol unit 137, and a transmission control unit 138.

The engine 131 has an output shaft connected to an input shaft of thetorque converter 132. The torque converter 132 has an output shaftconnected to the transmission 133. The torque converter 132 is awell-known fluid coupling including an impeller, a turbine, and astator. Rotation of the engine 131 is transmitted to the transmission133 via the torque converter 132. The transmission 133 includes ahydraulic clutch that changes shift speed positions of the transmission133. The transmission 133 changes speeds of rotation of the output shaftof the torque converter 132. Rotation after the speed change istransmitted to the front wheel 113 and the rear wheel 114 via apropeller shaft 141 and axles 142. This causes the wheel loader 100 torun.

The hydraulic pump 134 is a variable displacement type driven by theengine 131 to deliver hydraulic fluid. The hydraulic fluid deliveredfrom the hydraulic pump 134, while having its direction and flow ratecontrolled by the control valve 135, is supplied to work actuators, suchas the arm cylinder 123 and the bucket cylinder 124, thereby driving thework actuators. The control valve 135 is operated by an arm controllever 11 and a bucket control lever 12 (to be described later). Thecontrol valve 135 controls flow of the hydraulic fluid to the armcylinder 123 or the bucket cylinder 124 according to an operation signalfrom the arm control lever 11 or the bucket control lever 12. Thehydraulic pump 134 has a pump capacity varied by a regulator (notshown). The regulator varies the pump capacity according to the pumpdelivery pressure to thereby perform, for example, constant torquecontrol in which work torque remains constant. It is noted that a fixeddisplacement pump, such as a gear pump, may be used for the hydraulicpump 134.

The controller 136 is configured to include an arithmetic processingunit that includes a CPU, a ROM, a RAM, and other peripheral circuits.The controller 136 receives inputs of signals from an acceleratoroperation amount detector 143, a vehicle speed detector 144, a speeddetector 145, a speed detector 146, a forward/reverse changeover switch14, a shift speed position switch 15, kickdown switches 16, 17, a mainmode changeover switch 18 (hereinafter referred to as a “main switch18”), and a sub-mode changeover switch 19 (hereinafter referred to as a“sub-switch 19”). Specifically, the accelerator operation amountdetector 143 detects an operation amount of an accelerator pedal 13. Thevehicle speed detector 144 detects a rotational speed of the outputshaft of the transmission 133 (or the propeller shaft 141) as a vehiclespeed. The speed detector 145 detects a rotational speed Ni of the inputshaft of the torque converter 132. The speed detector 146 detects arotational speed Nt of the output shaft of the torque converter 132. Theforward/reverse changeover switch 14 selects a forward mode (F), areverse mode (R), or a neutral mode (N) of the wheel loader 100. Theshift speed position switch 15 specifies an upper limit of a shift speedposition among 1st to 4th speeds. The kickdown switches 16, 17 direct achangeover of the shift speed to a lower speed. The main switch 18selects a running mode of either a power mode (hereinafter referred toas a “P mode”) in which emphasis is placed on workability or an economymode (hereinafter referred to as an “E mode”) in which emphasis isplaced on fuel economy. The sub-switch 19 also selects the running modeof either the P mode or the E mode.

In the embodiment, each of the kickdown switches 16, 17 and thesub-switch 19 is a pushbutton switch having therein predetermined play.To prevent an operation signal from being output when a finger or a palmof an operator covers and slightly depresses the switch (to avoid anoperation unintended by the operator), the switch is designed to have acertain allowance so as not to output the operation signal unless theswitch is depressed a required stroke.

The torque converter 132 has a function of increasing output torquerelative to input torque, specifically, having a torque ratio of 1 ormore. The torque ratio decreases with an increase in a torque converterspeed ratio e (output rotational speed Nt/input rotational speed Ni),specifically, a ratio of the rotational speed of the input shaft to thatof the output shaft of the torque converter 132. When, for example,running load increases during running at a constant engine speed, theoutput rotational speed Nt of the torque converter 132, specifically,the vehicle speed decreases with a resultant small torque converterspeed ratio e. Since the torque ratio increases at this time, thevehicle can run with an even greater running driving force (tractionforce). Specifically, a low vehicle speed results in an increasingrunning driving force (low speed high torque) and a high vehicle speedresults in a decreasing running driving force (high speed low torque).

The transmission 133 is an automatic transmission having a clutch and asolenoid valve associated with each shift speed position of the 1st to4th speeds. Each of the solenoid valves is driven by a control signaloutput from the controller 136 to the transmission control unit 138,causing hydraulic fluid to act on a corresponding clutch to therebychange a clutch position. The controller 136 stores in advance therein atorque converter speed ratio e1 that serves as a reference forupshifting and a torque converter speed ratio e2 that serves as areference for downshifting. In an automatic transmission mode, thecontroller 136 calculates the torque converter speed ratio e usingsignals from the speed detectors 145, 146. If the calculated torqueconverter speed ratio e is greater than the torque converter speed ratioe1, the controller 136 outputs an upshift signal to the transmissioncontrol unit 138. If the calculated torque converter speed ratio e issmaller than the torque converter speed ratio e2, the controller 136outputs a downshift signal to the transmission control unit 138. Thisallows the shift speed position of the transmission 133 to beautomatically changed among the 1st to 4th speeds according to thetorque converter speed ratio e.

At this time, the shift speed position is automatically changed with theshift speed position selected with the shift speed position switch 15 asthe upper limit. For example, if the 2nd speed is selected with theshift speed position switch 15, the shift speed position is either the1st speed or the 2nd speed according to the torque converter speed ratioe. If the 1st speed is selected with the shift speed position switch 15,the shift speed position is fixed at the 1st speed. Though not shown,the arrangement may include a function that changes from the automatictransmission mode to a manual transmission mode and, in the manualtransmission mode, the shift speed position switch 15 or anotherseparately provided switch may be manually operated to select any shiftspeed position.

The kickdown switches 16, 17 forcibly effect a downshift to a lowershift speed position. Each time the kickdown switch 16 or the kickdownswitch 17 is operated once, the controller 136 outputs a downshiftsignal to the transmission control unit 138 to forcibly effect adownshift by one speed at a time regardless of the torque converterspeed ratio e. In the automatic transmission mode, operating thekickdown switch 16 or the kickdown switch 17 when, for example, thevehicle speed is low allows a downshift to be effected forcibly.

In the arrangement described above, an upshift or a downshift iseffected when the torque converter speed ratio e is greater or smallerthan the predetermined value e1 or e2. Alternatively, a gearshift mayeven be effected when the vehicle speed reaches a predetermined value.Such an arrangement can be achieved by, for example, causing an upshiftsignal or a downshift signal to be output to the transmission controlunit 138 according to a signal from the vehicle speed detector 144.

The controller 136 also brings the engine speed to a target engine speedaccording to the operation amount of the accelerator pedal 13.Specifically, a greater depression amount of the accelerator pedal 13results in an increased target engine speed and the controller 136outputs a control signal corresponding to the target engine speed,thereby controlling the engine speed.

FIG. 3 is a running performance diagram (torque diagram) showing arelation between the engine speed and torque when the accelerator pedal13 is fully depressed.

In FIG. 3, characteristics Ap and Ae are torque diagrams when therunning mode is the P mode and the E mode, respectively. Whereas theengine maximum speed is not limited in the P mode, the engine maximumspeed is limited in the E mode to a point on the low speed side.

Characteristics B0 to B2 are exemplary input torque values when thetransmission 133 is driven by the engine 131, indicating that the inputtorque increases with an increasing engine speed. This input torqueincludes input torque of the hydraulic pump 134 and varies as shown bythe characteristics B0 to B2 according to the torque converter speedratio e and suction torque of the hydraulic pump 134. Specifically, asmaller torque converter speed ratio e results in greater input torque(the characteristic B0) and a greater torque converter speed ratio eresults in smaller input torque (the characteristic B2).

An intersection between the characteristic Ap/Ae and the characteristicB0/B1/B2 is a matching point and the engine speed is the value of thematching point. Thus, the engine speed relative to predetermined inputtorque is higher in the P mode than in the E mode. With the engine speedat the matching point, the running driving force is proportional to thesquare of the engine speed N. Thus, the running driving force is greaterin the P mode than in the E mode and a maximum vehicle speed at eachshift speed is faster by a margin of the higher engine speed.

FIG. 4 is a graph showing a relation between the vehicle speed and therunning driving force at each of different shift speeds. In FIG. 4,solid lines represent characteristics in the P mode and dotted linesrepresent characteristics in the E mode.

A comparison made at the same shift speed in FIG. 4 reveals that therunning driving force is greater at a lower vehicle speed (low speedhigh torque) and smaller at a higher vehicle speed (high speed lowtorque). Additionally, the lower the shift speed position, the greaterthe running driving force obtained at the same vehicle speed.Specifically, the maximum running driving force is greater and themaximum vehicle speed is higher in the P mode than in the E mode. At the2nd speed position, for example, a maximum running driving force F2 inthe P mode is greater than a maximum running driving force F2′ in the Emode and a maximum vehicle speed V2 hi in the P mode is higher than amaximum vehicle speed V2′hi in the E mode.

FIG. 5 is a plan view showing a configuration of the cabin 116.

A side console panel 22 and a work implement control device 20 aredisposed on the right of a driver's seat 21. A front panel 23 forward ofthe driver's seat 21 includes a steering wheel 27, the forward/reversechangeover switch 14, and a monitor panel 24. The monitor panel 24includes a display 25 that indicates whether the E mode or the P mode isselected. The forward/reverse changeover switch 14 has the shift speedposition switch 15 disposed at a leading end thereof. In addition, theaccelerator pedal 13 and right and left brake pedals 26 are disposedforwardly of the driver's seat 21 and downwardly of the front panel 23.

The abovementioned mode changeover main switch 18 (see FIG. 6 also) isdisposed on the side console panel 22. The main switch 18 is analternate switch that is placed in either a P position indicating the Pmode or an E position indicating the E mode. The work implement controldevice 20 is disposed forwardly of the side console panel 22. The workimplement control device 20 includes the bucket control lever 12 thatdirects an operation of the bucket cylinder 124, the arm control lever11 that directs an operation of the arm cylinder 123, the sub-switch 19that selects either the E mode or the P mode, the two modes having anengine maximum speed upper limit value different from each other, andthe two kickdown switches 16, 17 that forcibly effect a downshift.

FIG. 7 is a schematic rear elevational view showing an appearance of thework implement control device 20.

As shown in FIG. 7, the arm control lever 11 is in juxtaposition on theright with the bucket control lever 12 disposed on the right-hand sideof the driver's seat 21. The kickdown switches 16, 17 described earlierare disposed at an upper surface (apex) and a left side surface (theside surface on the side of the driver's seat 21) of a grip 11 a of thearm control lever 11. The mode changeover sub-switch 19 describedearlier is disposed at a left side surface (the side surface on the sideof the driver's seat 21) of a grip 12 a of the bucket control lever 12.The sub-switch 19 may be disposed at an upper surface of the grip 12 aof the bucket control lever 12 instead of, or in addition to, the leftside surface of the grip 12 a of the bucket control lever 12(specifically, the sub-switch 19 may be disposed only at the uppersurface (apex) of the grip 12 a, or at the upper surface and the leftside surface of the grip 12 a as with the kickdown switches 16, 17). Thearm control lever 11 further includes a detent mechanism 11 b(schematically shown in FIG. 2) that maintains posture at a position atwhich an arm raising operation is directed.

As described earlier, the kickdown switches 16, 17 and the sub-switch 19are each a pushbutton switch and, in this embodiment, are each analternate pushbutton. Thus, each time either one of the kickdownswitches 16, 17 is operated once during running at a shift speedposition other than the 1st speed (if there exists any other lower shiftspeed position), the controller 136 outputs a downshift signal to thetransmission control unit 138 according to the operation signal and adownshift is effected one speed position each to a lower speed. Ifeither one of the kickdown switches 16, 17 is operated at the 1st shift,the shift speed position selected with the shift speed position switch15 is reselected. If, however, the 1st speed is selected with the shiftspeed position switch 15, no gearshift is effected from the 1st speedregardless whether the kickdown switches 16, 17 are operated. Theoperation on the sub-switch 19 is accepted by the controller 136, onlyif the E mode has been selected with the main switch 18. Specifically,when the P mode has been selected with the main switch 18, the runningmode is fixed in the P mode and operating the sub-switch 19 does notcause the controller 136 to output a running mode changeover signal tothe engine control unit 137, so that the running mode is not to bechanged to the E mode. At this time, the maximum speed of the engine 131is not limited and the running driving force and the vehicle speed canbe maximized within the capacity of the engine 131. If the E mode hasbeen selected with the main switch 18, on the other hand, the depressionof the sub-switch 19 during running causes the controller 136 to outputa mode changeover signal to the engine control unit 137, thus changingthe running mode to the P mode. If the sub-switch 19 is then depressed asecond time, the running mode is returned to the E mode. In the E mode,the maximum speed of the engine 131 is limited to the low speed side, sothat the maximum running driving force and the maximum vehicle speed arelimited, thus improving fuel economy. Thereafter, too, each time thesub-switch 19 is operated with the main switch 18 in the E position, therunning mode is repeatedly changed to the P mode, the E mode, the Pmode, . . . .

A typical sequence of excavating operations performed by the wheelloader having the arrangements as described heretofore will be describedbelow.

FIG. 8 is a schematic view showing how material to be excavated, such assand and gravel, is scooped up during loading of the material onto, forexample, a dump truck using the wheel loader 100.

As shown in FIG. 8, when the material to be excavated is to be scoopedup, typically, (A) the wheel loader 100 moves forward at, for example,the 2nd speed toward a mound P of the material to be excavated(hereinafter referred to simply as the “mound P”) and approaches themound P. At this time, the main switch 18 is placed in the E positionand the E mode is selected for the running mode. Then, (B) the armcontrol lever 11 and the bucket control lever 12 are operated to lowerthe arm 121 and face an open mouth of the bucket 122 forward;immediately before penetration into the mound P, the kickdown switch 16or 17 is depressed to kick down from the 2nd speed to the 1st speed. Thekickdown to the 1st speed is to allow a large running driving forcerequired for loading the material in the bucket 122 to be extracted.

Upon penetration into the mound P, (C) the arm raising operation isretained using the detent mechanism 11 b of the arm control lever 11.This allows the arm 121 to continue performing the arm raising operationeven when the operator releases the arm control lever 11. During the armraising operation, the bucket control lever 12 is operated to crowd thebucket 122 to thereby scoop up and capture the material to be excavatedin the bucket 122. When the material is to be scooped up and captured,the amount of depression of the accelerator pedal 13 is appropriatelyvaried to thereby adjust the running driving force (traction force). Itis to be noted at this time that the running driving force may be betterto be held below a predetermined level or increased to a greater leveldepending on the property of the material to be excavated or the roadsurface condition during the scooping and capturing operation. Theoperator thus needs to scoop and capture the material to be excavated inthe bucket 122 by selecting the E mode or the P mode as appropriatedepending on the situation to prevent the road surface from being gougedby a slipping wheel. When the material has been captured in the bucket122, the operator (D) operates the forward/reverse changeover switch 14to select a reverse motion and reverses to be moved away from the moundP; the operator then reselects a forward motion to move to a locationnear a dump truck (not shown) and, operating the arm control lever 11and the bucket control lever 12, dumps the material into, for example, acargo deck of the dump truck.

It is noted that the selection of the E mode or the P mode as therunning mode is displayed on the display 25 forward of the driver's seat21 by a display signal output from the controller 136 based on anoperation signal from the main switch 18 and the sub-switch 19.

The embodiment can achieve the following effects.

(1) Improved Operability

As described above, when a large running driving force is temporarilyrequired, the depression of the sub-switch 19 allows the running mode tobe changed to the P mode. This eliminates the need for releasing thework implement control device 20 and operating the main switch 18 of theside console panel 22 to thereby select the P mode during the excavatingoperation. This achieves good workability. In addition, the depressionof the sub-switch 19 allows the running mode to be instantly changed tothe P mode regardless of the shift speed position. This is useful when,for example, increasing the running driving force temporarily duringrunning on an uphill road at the 2nd speed. Even after the running modehas been changed to the P mode through the operation on the sub-switch19, a second operation on the sub-switch 19 can return the running modeback to the E mode. The operator can therefore change the running modeas desired with the main switch 18 left in the E position. Mode changingoperations can thus be performed promptly and easily and the runningdriving force can be flexibly controlled.

It is here noted that, in general, different operators hold onto thegrip 11 a of the arm control lever 11 in different manners: some mayfirmly grip or hold only lightly onto the grip 11 a, others may grip thegrip 11 a from above or from a side. How the grip 11 a is held variesdepending on situations and preference of each individual operator. Inthe embodiment, therefore, the bucket control lever 12 is disposed onthe left-hand side near the operator, and the arm control lever 11 isdisposed on the right-hand side farther away from the operator; thekickdown switches 16, 17 for forcibly effecting a downshift are disposedat the upper surface and the left side surface (specifically, the sidesurface closer to the driver's seat), respectively, of the grip 11 a ofthe arm control lever 11, to thereby allow either one of the kickdownswitches 16, 17 to be operated for performing the kickdown operation. Asa result, if the grip 11 a is gripped from the above, the kickdownswitch 17 disposed at the left side surface of the grip 11 a can be moreeasily operated with the thumb of the right hand that is located on theleft side of the grip 11 a; if the grip 11 a is gripped from a side (theright-hand side), the kickdown switch 16 disposed at the upper surfaceof the grip 11 a can be more easily operated with the thumb of the righthand. Disposing the two kickdown switches 16, 17 on the upper surfaceand the left side surface, respectively, of the grip 11 a of the armcontrol lever 11 as described above enables a downshift operation to beperformed easily regardless of how the grip 11 a is gripped.

When the material to be excavated is to be scooped up by the bucket 122,operations of crowding the bucket, raising the arm, and moving the wheelloader forward need to be performed in parallel with each other. Whenthe detent mechanism 11 b of the arm control lever 11 is to be used forthe arm raising operation, the operator tends to let go of the armcontrol lever 11 and grip the grip 12 a from above to thereby operatethe bucket control lever 12. A large running driving force can berequired as appropriate depending on the situation during the operationof the bucket control lever 12. Even in such a case, the bucket controllever 12 that is being operated has the mode changeover sub-switch 19,so that the sub-switch 19 can be operated even with the bucket controllever 12 held in hand. This eliminates the need for releasing the workimplement control device 20 or holding a different control lever inorder to change the running mode. Moreover, the sub-switch 19 disposedat the left side surface of the grip 12 a facilitates a running modechangeover operation to be performed with the thumb of the right handplaced on the grip 12 a.

Locations and the number of kickdown switches 16, 17 and the runningmode changeover sub-switch 19 are optimized by disposing these switchesappropriately on the arm control lever 11 and the bucket control lever12 in consideration of actual excavating work of the material to beexcavated as described above. Operability can thereby be improved evenfurther. In addition, disposing the kickdown switches 16, 17 and therunning mode changeover sub-switch 19 appropriately on the arm controllever 11 and the bucket control lever 12, respectively, reduces thelikelihood of confusing the kickdown operation with the running modechangeover operation, thereby containing erroneous operations.

As described above, the embodiment can improve operability even further.

In addition, a need may arise to increase the running driving forcetemporarily as when, for example, climbing an uphill road during runningat times other than the excavating work when the work implement controldevice 20 is not to be operated. The running mode changeover operationcan be performed easily even at such a time, because the mode changeoversub-switch 19 is disposed on the bucket control lever 12 that is closerto the operator. This is useful for achieving good operability.

(2) Effect of Alternate Switches

The kickdown switches 16, 17 and the mode changeover sub-switch 19 areeach an alternate switch. Any shift speed position or any running modecan therefore be selected individually for each of the switches 16, 17,19. This arrangement can reduce space requirements for the variousdevices for performing the kickdown operation and the running modechangeover operation. The switches 16, 17, 19 can thus be disposedsuitably in small spaces of the grips 11 a, 12 a of the arm controllever 11 and the bucket control lever 12. Being able to dispose theswitches 16, 17, 19 on the grips 11 a, 12 a in the above-describedmanner greatly contributes to achieving the abovementioned highoperability. Each of the switches 16, 17, 19, being the alternateswitch, is easy to operate, allowing the running mode or the shift speedposition to be set as desired with a single switch. This is advantageousas compared with a case in which an arrangement includes a plurality ofkickdown switches, each being used to directly select a correspondingshift speed position, or in which an arrangement includes twosub-switches, one for selecting the E mode and the other for selectingthe P mode.

(3) Achieving good Running Mode Determining Performance

The selected running mode is displayed on the display 25 of the monitorpanel 24 as required. The operator is thus able to determine the runningmode on the display 25 as necessary even if the running mode isfrequently changed with the sub-switch 19. This allows the operator toperform operations while determining the running mode as necessary, sothat he or she can easily set the running mode according to his or herintention. An erroneous operation can thus be prevented. Specifically,for example, when the operator mistakenly perceives that the E mode isselected when the P mode is actually selected and depresses theaccelerator 13, resulting in the increasing running driving forceagainst the intention of the operator and gouging the road surface.

The above embodiment has been exemplarily described with respect to anarrangement in which the running mode changeover sub-switch 19 isdisposed only at the left side surface of the grip 12 a of the bucketcontrol lever 12. This is, however, not the only possible arrangement;alternatively, the sub-switch 19 may be disposed only at the uppersurface of the grip 12 a or at each of the upper surface and the leftside surface (two sub-switches 19 in total). Assuming that the grip 12 aof the bucket control lever 12 is gripped from a side, the modechangeover sub-switch 19 disposed on the upper portion of the grip 12 aof the bucket control lever 12 can be easily depressed with the thumb ofthe right hand. If different operators grip the bucket control lever 12differently, it is useful to have the sub-switches 19 on the uppersurface and the left side surface of the grip 12 a of the bucket controllever 12.

Although the sub-switch 19 of an alternate type has been exemplarilydescribed, a momentary switch of the same pushbutton type may be usedbecause of an intended use of the sub-switch 19 for a temporary andshort-period changeover of the running mode. If a momentary switch isused for the sub-switch 19 and when the sub-switch 19 is depressed withthe E mode selected with the main switch 18, the controller 136 outputsa mode changeover signal to the engine control unit 137 according to theoperation signal. The running mode is changed to the P mode as long asthe sub-switch 19 is held down and, when the depression of thesub-switch 19 is stopped, the running mode is returned to the E mode.

The embodiment has been described such that the output of a controlsignal from the controller 136 to the engine control unit 137 does notcause the maximum speed of the engine 131 to be limited when the P modeis selected, but causes the maximum speed of the engine 131 to belimited in the E mode to a point on the low speed side. However, theengine maximum speed in the P mode needs only to be shifted to a higherspeed side than the engine maximum speed in the E mode and the enginemaximum speed in the P mode is not necessarily to be unlimited. Theembodiment has also been described to include the E mode and the P modefor the running mode. The running mode may still include three or moremodes having different engine maximum speed upper limit values. In thiscase, preferably, each press of the sub-switch 19 changes the runningmode in sequence in the same manner as with the shift speed positionbeing changed one speed position each time the kickdown switch 16 or 17is operated once.

The embodiment has been described so that the speed detectors 145, 146detect the torque converter speed ratio e; however, the speed ratiodetecting device may have any configuration. The rotation of the engine131 has been described to be transmitted to the front wheel 113 and therear wheel 114 via the torque converter 132, the transmission 133, thepropeller shaft 141, and the axles 142. The mechanism for transmittingthe running driving force may nonetheless have any configuration.

Not only the kickdown switches 16, 17, but also the sub-switch 19 as themode changeover switch can be disposed at two places on the uppersurface and the side surface adjacent to the driver's seat 21 of thegrips of the control levers, as described earlier. The downshiftoperation using the kickdown switches 16, 17 and the gearshift operationusing the sub-switch 19 are commonly related to each other as anoperation associated with the traction force. An arrangement in whichtwo sub-switches 19 are disposed at two places of the grip cancontribute to improved operability during scooping of sand or the likedepending on operator conditions.

Additionally, the embodiment has been described for an exemplary case inwhich the arm control lever 11 and the bucket control lever 12 aredisposed on the right of the driver's seat 21. Nonetheless, the armcontrol lever 11 and the bucket control lever 12 may still be disposedon the left of the driver's seat 21. Furthermore, preferably, the bucketcontrol lever 12 is disposed on the side of the arm control lever 11adjacent to the driver's seat 21. An arrangement is nonetheless possiblein which the arm control lever 12 is disposed on the side adjacent tothe driver's seat 21.

At this time, of the kickdown switches 16, 17 and the sub-switch 19,those to be disposed at the side surface of the grip 11 a of the armcontrol lever 11 and the side surface of the grip 12 a of the bucketcontrol lever 12 are to be disposed at the side surfaces of the grips 11a, 12 a adjacent to the driver's seat 21, because those switches areintended to be operated with the thumb when the grips are gripped fromthe above as described earlier. If the arm control lever 11 and thebucket control lever 12 are disposed on the left of the driver's seat21, therefore, the kickdown switches 16, 17 are to be disposed at theupper surface and the right side surface of the grip 11 a of the armcontrol lever 11. Similarly, if the sub-switch 19 is to be disposed at aside surface of the grip 12 a of the bucket control lever 12 disposed onthe left of the driver's seat 21, the sub-switch 19 is disposed at theside surface of the grip 12 a adjacent to the driver's seat 21,specifically, the right side surface of the grip 12 a.

DESCRIPTION OF REFERENCE NUMERALS

-   11 Arm control lever-   11 a Grip-   11 b Detent mechanism-   12 Bucket control lever-   12 a Grip-   16, 17 Kickdown switch-   19 Sub-switch (mode changeover switch)-   20 Work implement control device-   21 Driver's seat 21-   25 Display (display means)-   100 Wheel loader-   110 Vehicle body-   113 Front wheel-   114 Rear wheel-   120 Work implement-   121 Arm-   122 Bucket-   123 Arm cylinder-   124 Bucket cylinder

1. A wheel loader comprising: a vehicle body having a wheel; a workimplement disposed at a front portion of the vehicle body; and a workimplement control device for directing an operation of the workimplement, the work implement control device comprising: a control leverdisposed on a side of a driver's seat, the control lever being used fordirecting an operation of the work implement; and two switches disposedat an upper surface and a side surface of a grip of the control lever,the side surface of the grip being on a side adjacent to the driver'sseat, the two switches being used for performing operations associatedwith a traction force.
 2. The wheel loader according to claim 1, whereinthe work implement includes an arm, a bucket, and an arm cylinder and abucket cylinder for driving the arm and the bucket, respectively, andthe work implement control device includes: an arm control lever servingas the control lever, the arm control lever being used for directing anoperation of the arm cylinder; a bucket control lever in juxtapositionto the arm control lever on a side adjacent to the drivers seat, thebucket control lever being used for directing an operation of the bucketcylinder; two kickdown switches that are the two switches disposed atthe upper surface and the side surface of the grip of the arm controllever, the side surface of the grip being on the side adjacent to thedrivers seat, the two kickdown switches being used for forciblyeffecting a downshift of a shift speed position; and a mode changeoverswitch disposed at a side surface of a grip of the bucket control lever,the side surface of the grip being on a side adjacent to the driver'sseat, the mode changeover switch being used for changing over aplurality of running modes having different engine maximum speed upperlimit values from each other.
 3. The wheel loader according to claim 2,wherein the mode changeover switch is disposed at an upper surface ofthe grip of the bucket control lever, in place of, or in addition to,the side surface of the grip of the bucket control lever adjacent to thedriver's seat.
 4. The wheel loader according to claim 2, wherein themode changeover switch is a pushbutton for individually directing achangeover of a plurality of running modes having different enginemaximum speed upper limit values from each other.
 5. The wheel loaderaccording to claim 2, further comprising: display means for displaying arunning mode selected with the mode changeover switch.
 6. The wheelloader according to claim 2, further comprising: a detent mechanism formaintaining posture of the arm control lever at a position at which anarm raising operation is directed.
 7. The wheel loader according toclaim 3, wherein the mode changeover switch is a pushbutton forindividually directing a changeover of a plurality of running modeshaving different engine maximum speed upper limit values from eachother.
 8. The wheel loader according to claim 3, further comprising:display means for displaying a running mode selected with the modechangeover switch.
 9. The wheel loader according to claim 4, furthercomprising: display means for displaying a running mode selected withthe mode changeover switch.
 10. The wheel loader according to claim 3,further comprising: a detent mechanism for maintaining posture of thearm control lever at a position at which an arm raising operation isdirected.
 11. The wheel loader according to claim 4, further comprising:a detent mechanism for maintaining posture of the arm control lever at aposition at which an arm raising operation is directed.
 12. The wheelloader according to claim 5, further comprising: a detent mechanism formaintaining posture of the arm control lever at a position at which anarm raising operation is directed.